Field instruments (e.g., valve positioners) are used in a wide variety of environments for both commercial and industrial applications. Because of their varied use, field instruments often operate in remote areas and/or hazardous environments in which supply power is not readily available. In these instances, and numerous others, many field instruments obtain at least part of their power from their control signaling system (e.g., a 4-20 mA system). This power may be used to operate a variety of electronic components of the field instrument, including sensors, actuators, controllers, and transceivers.
For a variety of reasons (e.g., power consumption, reliability, and safety), it is typically desirable to operate the electronic components of a field instrument at a lower voltage than its control signaling system (e.g., 10 V versus 24 V). Typical devices for down-converting the voltage in a field instrument are switched-capacitor voltage converters and linear voltage converters.
Unfortunately, control signaling systems often have relatively low powers (e.g., <2 W), and with the increasing number and complexity of electronic components used in field instruments, sufficient power may not be available using current power derivation techniques.